Cooling systems

ABSTRACT

Cooling of an enclosed space is effected by a cooling system including a plurality of cooling units forming ducts having an internal surface on which a layer of liquid is developed, e.g. by a wicking material, and through which air from the enclosed space is passed in contact with the liquid layer whereby the liquid is exposed to and evaporates into the air-flow with consequent cooling of the duct wall on which the liquid layer is developed.

This application is the national phase under 35 USC §371 of PCTInternational Application No. PCT/GB01/04532 which has an Internationalfiling Date of Oct. 11, 2001, which designated the United States ofAmerica and was published in English and claims priority from 0025279.1filed Oct. 14, 2000 in Great Britain which is claimed herein.

FIELD OF THE INVENTION

This invention relates to systems for cooling an enclosed space, for usefor example in air conditioning and displacement ventilation systems.

BACKGROUND OF THE INVENTION

Air conditioning, radiant surface and displacement ventilation systemsare used in enclosed spaces such as buildings, vehicles and equipmenttrailers, to provide cooling for equipment and thermal comfort forpeople. This is achieved by providing an adequate flow of air to theenclosed space with the air supply, when necessary, having been cooledand dehumidified; a typical state for the supplied air could be 13° C.and 65% relative humidity. In conventional systems, the thermal load ofthe space is dissipated entirely by using sensible heat transfer intothe air stream and this determines the required air flow rate for thespace; a typical state for the air leaving the space could be 24° C. and35% relative humidity.

The low value of the relative humidity in the exhaust air represents anunused cooling potential that can be used, via latent heat transfer, tosubstantially increase the capacity of the air stream to remove thermalenergy from the space. This potential cannot be realised by directevaporation into the space because the increased humidity would reducethe comfort condition for occupants and any wet surfaces could representa hazard with electrical equipment.

SUMMARY OF THE INVENTION

It is an objective of the present invention to utilise the extra coolingpotential of the low relative humidity exhaust air from an airconditioned or ventilated space to increase the thermal energy removedfrom the space.

According to one aspect of the present invention there is provided acooling system for an enclosed space comprising: a ceiling, floor orwall (hereinafter referred to as “surface structure”) bounding theenclosed space, means for developing a layer of liquid on a face of thesurface structure remote from the space, and means for exhausting airfrom the space and passing the exhausted air over said remote face sothat, in use, the exhaust air effects evaporation of liquid from saidlayer into the air flow.

In this manner, cooling of the surface structure is effected thusallowing thermal energy to be extracted from a space bounded by suchstructure.

Preferably means is provided for replenishing the layer of liquid as itevaporates. Means may also be provided for collecting excess liquid.

The liquid layer is preferably developed using a layer of wickingmaterial which may be in sheet form.

The layer of wicking material may be a single continuous layer or it maycomprise a number of separate sheets, at least some of which may beinterconnected with each other. Where the wicking material issub-divided into a number of separate sheets, at least some of thesheets may share a common liquid feed and/or collector.

The wicking material will usually be in direct contact with said remotesurface.

The surface structure may comprise a plurality of structural units whichmay be arranged in serial fashion and/or side by side fashion. The unitsmay be of elongated configuration, viz. forming a strip-like unit. Notall of the structural units forming the ceiling or wall or otherstructure need be cooling units. For instance, the cooling function maybe confined to one or more areas of the overall surface.

Each structural unit may include a further surface in spaced, opposedrelation to said remote face to form an air flow path across said remoteface. The air flow path may traverse the remote face from an inlet to anoutlet of the unit.

The internal face of each cooling unit may be provided with a layer ofwicking material and at least some of the cooling units may beinterconnected so that liquid flow is conducted from one unit to thenext. Also each cooling unit may include a chamber for discharge of airafter passage over the liquid layer and such chambers of at least someof the units may be interconnected to form an air discharge duct.

According to a second aspect of the present invention there is provideda unit forming an air-flow channel and comprising a wall having internaland external faces, means for developing a layer of liquid on theinternal face for exposure to and evaporation into the air-flow andmeans for supplying liquid to the liquid layer-developing means tomaintain the internal surface wetted.

The unit may include a further surface in spaced, opposed relation tosaid internal surface to form an air flow path across said internalface. The arrangement may be such that the cross-sectional area of theair flow path over the wetted internal face varies in the direction ofair flow, e.g. it may progressively reduce in the downstream direction.

Each unit may be provided with a liquid collector for collecting excessliquid from the unit The liquid supply and/or liquid collector may beadapted for connection to the corresponding supply and collector ofother units, e.g. through male and female connectors.

The means for developing a liquid layer preferably includes a layer ofwicking material provided on the internal face of the unit, e.g. a sheetof wicking material.

Liquid supply to and/or collection from the wicking layer may be by wayof wicking element(s) associated with opposite edges of the wickinglayer.

The wicking element(s) may be of greater cross-section than the layer ofwicking material.

The unit may comprise a first lower chamber in which air flows over theliquid layer and a second upper chamber through which the air isexhausted after passage over the liquid layer.

According to a further aspect of the present invention there is provideda method of cooling an enclosed space bounded by at least one surfacestructure such as a wall or ceiling structure, said method comprisingthe steps of: developing a layer of liquid on a surface of saidstructure which is remote (viz external to) said space; removing airfrom the space and contacting the same with the liquid layer so thatevaporation of liquid from the liquid layer into the air flow is securedthereby cooling said structure and hence the space bounded thereby.

The liquid may be water and an additive may be added to the liquid toinhibit microbial growth. The additive used to inhibit microbial growthmay be sodium chloride or sodium hypochlorite.

Sea water may be used as the wetting liquid and the vapour entrained inthe air flow may be collected and condensed for use as fresh water.

The invention will now be described by way of example only withreference to the accompanying diagrammatic drawings, in which:

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a conditioned space provided with a cooling system inaccordance with the invention;

FIG. 2 shows one arrangement for feed and discharge of liquid to thesystem;

FIG. 3 is a longitudinal section of a ceiling tile which forms part ofone form of cooling system in accordance with the present invention;

FIG. 4 is a cross section of a ceiling tile, showing a particulararrangement of the supply and collection wicks;

FIG. 5 is a cross section showing mounting of a ceiling tile within asuspended ceiling structure;

FIG. 6 illustrates a means of obtaining a uniform flux and temperatureprofile along a tile or ceiling;

FIG. 7 illustrates alternative means of constructing supply and exhaustpipes;

FIG. 8 illustrates a further embodiment of the invention;

FIG. 9 illustrates another embodiment of the invention in which thecooling effect is achieved by means of one or more ducts;

FIG. 10 is an overhead view of the plenum chamber and bank of ducts seenin FIG. 9;

FIG. 11 is tnansverse sectional view of one of the ducts in FIGS. 9 and10;

FIG. 11A is a fragmentary view corresponding to that of FIG. 11 butillustrating a modification;

FIG. 12 is a fragmentary view corresponding to part of the arrangementof FIG. 9 but illustrating another modification;

FIG. 13 is a fragmentary overhead view illustrating use of the use ofone delivery tube for each pair of adjacent ducts;

FIG. 14 is a view illustrating a delivery or collector tube providedwith shrink tube fittings at the ends thereof; and

FIG. 15 is a sectional view showing one way of forming a tubular wickingstructure for use as a delivery or collector tube in accordance with theinvention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The invention is illustrated schematically in FIGS. 1 and 2 and isimplemented in a false ceiling or wall that is dry on the side facingthe conditioned or ventilated space to be cooled but wet on the faceremote from that face, exhaust air from the space to be cooled beingpassed over the wetted surface so that evaporative cooling of theceiling or wall is effected. Such evaporative cooling of the ceiling orwall in turn removes thermal energy from the conditioned or ventilatedspace, e.g. by radiation and convection heat transfer to the dry side ofthe false ceiling or wall.

Referring more specifically to FIGS. 1 and 2, cooled air 1 from an airconditioning system (not shown) enters space 2 through inlet 29 whilewarmer relatively low humidity exhaust air 4 from space 2 may at leastin part be returned to the air conditioning system through outlet 28 viaa passageway above the false ceiling 32. Alternatively the exhaust air 4may be dumped. The lower face 3 of the false ceiling is presentedinteriorly of the space 2 while the upper face is remote from the space2. The remote or upper face of the ceiling is maintained wetted by meansof liquid (usually water, possibly with additives) supplied to a layer 5of wicking material which extends over at least part of the ceiling(e.g. a major part thereof) in contact with the remote face of theceiling 32. The wicking material may be any suitable material which iscapable of developing a layer of liquid over the desired region of theceiling, e.g. a fabric material such as cotton cloth.

Liquid is supplied to the layer 5 from a reservoir 6 via a supply feed 8(see FIG. 2) which extends over a substantial dimension of the layer 5from one end to the other. In FIG. 2, the feed 8 is located along oneside of the layer 5 so that liquid is transferred into the layer 5 atthat side and then traverses the width of the layer to the opposite sideby capillary action. During such traverse, the liquid wets the layer 5and hence the remote face of the ceiling thereby maintaining the latterconstantly wetted. Part of the liquid is evaporated from the layer 5 bythe flow of relatively warm, relatively low humidity exhaust air 4. Theexcess liquid reaching the opposite side of the layer 5 is drained by acollector 9 and routed into a container 7. The feed 8 and the collector9 in the embodiment of FIGS. 1 and 2 are in the form of elongatedelements of increased cross-section relative to the sheet of wickingmaterial forming the layer 5 and may comprise a wicking material (e.g.the same wicking material as that constituting the layer 5). The feed 8and collector 9 may each be formed for instance by tightly rolling orfolding a strip or sheet of wicking material to produce a thickercross-section than the layer 5. The feed 8 and collector 9 are suitablycontacted or connected with the respective sides of the layer 5 toensure uninterrupted flow into and from the layer 5.

The excess liquid collected in the container 7 may be disposed of orreturned to reservoir 6 for re-use. Supply reservoir 6 is connected to awater supply (not shown) to maintain a head of water. A water levelcontroller such as a ball-cock arrangement may be used to control theflow of water into supply reservoir 6. The collector 9 terminates at apoint below the liquid level in supply reservoir 6 and allows drips tobe collected in container 7. The flow rate of water through wickinglayer 5 is then determined by the difference in height between theliquid level in supply reservoir 6 and the end of exhaust pipe 9 abovecollection container 7, together with the hydraulic resistance throughthe complete structure. Water in reservoir 6 is maintained at a levelbelow the level of wicking layer 5 distributed across false ceiling 32and this prevents the possibility of any drips forming on lower ceilingsurface 3. Alternatively, reservoir 6 may be placed above ceiling wick 5if, for instance, ceiling 32 is designed to prevent dripping and theliquid flow rate is controlled to lie within the flow rate capacity ofwicking layer 5.

The arrangement thus far described is particularly suitable for the casewhere the liquid includes a soluble solid additive (e.g. a biocide suchas NaCl). Where no such additive is used or if the additive is liquid,e.g. a liquid biocide, such that there is no risk of crystallisation ofthe solute, the collector 9 and the container 7 may be omitted.

In use, dehumidified cooled air 1 is introduced through inlet 29 intothe air-conditioned or ventilated space 2 underneath the false ceiling32. Exhaust air 4 from space 2 passes over the layer 5 which maintainsthe upper or remote face of the ceiling constantly wet while the lowerface 3 of the ceiling remains dry. The state of cooled air 1 enteringthe space 2 is typically 13° C. and 65% relative humidity and that ofexhaust air 4 as it leaves space 2 is typically 24° C. and 35% relativehumidity. Water evaporates from the layer 5 into exhaust air 4, therebycooling the false ceiling 32 through contact between the layer 5 and theupper face of the ceiling. As a result, the cooled false ceiling 32extracts thermal energy from conditioned space 2, e.g. by radiation andconvective heat transfer.

Water in reservoir 6 is typically at room temperature and all additionalcooling is provided by evaporation of water from the wicking layer 5.This is in contrast to conventional chilled ceilings, which requireseparate chilled water units to supply water at about 12° C. or less.Conventional cooling panels, such as those used for chilled ceilings,require the use of low water temperatures and materials of high thermalconductivity because the thermal energy flow path is long and the fluxis concentrated as it travels through the panel from the space to thecooling water. In the cooling system of this invention, the thermal fluxmay remain at a substantially uniform density and the flow path from thespace 2 to the evaporating water may be short so that materials of lowthermal conductivity and cost, such as plastic, can be used forconstruction. The condensation formed on the pipes carrying the chilledwater in conventional cooling panels also causes a problem and meanshave to be found to deal with the condensation to avoid drips into thespace being cooled.

In FIGS. 1 and 2, the wicking layer 5 is shown as a single continuoussheet extending over a substantial part of the ceiling. In theembodiment of FIG. 3, the wicking layer 5 is effectively sub-dividedinto a number of smaller areas by for instance embodying the arrangementwithin ceiling tiles used to construct the false ceiling. FIG. 3illustrates one such tile unit or module and it will be understood thatthe ceiling as a whole or at least one or more regions thereof may beconstructed using such tiles which will be substantially of identicalconstruction and appearance and may be produced from appropriately rigidplastics material. The illustrated tile 11 is generally of box-sectionand has a bottom wall 50, the lower surface 3 of which, in use, isexposed to the space being cooled (i.e. space 2 in FIG. 1). On itsinterior surface (viz. the surface remote from the space 2 to becooled), the wall 50 is provided with a layer 5 of wicking material sothat a layer of liquid can be developed across the remote surfaceinternally of the tile.

The tile 11 has a top wall 52 spaced above the bottom wall 50 withfront, rear and side walls 54 extending between the bottom and top walls50, 52. The front and side walls 54 are not illustrated. An intermediatewall 56 is located between the top and bottom walls and divides theinterior of the tile into a lower chamber 58 and an upper chamber 60.Air is admitted from space 2 via an inlet or inlets 18 and the chambers58, 60 are interconnected by one or more apertures 19 so that air canflow from lower chamber 58 after passage over the wicking layer 5 intothe upper chamber 60. The upper chamber is provided with openings 20 and21 at opposite ends thereof. These openings are of complementaryconfiguration so that two tiles can be fitted together in sealed fashionwith the opening 20 of one tile in registry with the opening 21 of anadjacent tile. Thus, the openings may be arranged to interconnect by wayof male and female connector formations such as depicted by referencenumerals 62, 64. In this manner, the upper chambers 60 of two or moretiles can be interconnected to form a continuous duct extending thelength of the tiles which are so interconnected.

Continuity between the wicking layers 5 associated with each tile isachieved by means of male and female connectors 22, 23 so arranged thatthe connector 22, 23 of one tile sealingly engages with its counterparton an adjacent tile. At one end of a row of tiles interconnected in thisway, liquid is supplied by a feed arrangement to the inlet connector 22so that a layer of liquid can be developed on the interior face of thelower walls 50 of the tiles. At the opposite end of the row, the outletconnector 23 is connected to a collector for removal of excess liquid.The feeder and collector will each be associated with a supply reservoirand container corresponding to those depicted by references 6 and 7 inFIGS. 1 and 2 and the arrangement will be such that the formation ofdrips on the lower face of the wall 50 is avoided, as described inrelation to FIGS. 1 and 2.

Air flow from the space to be cooled is drawn into the tiles byconnection of the downstream ends of the ducts to the air return duct ofthe air conditioning or ventilating system. Thus, air enters via inlets18 of the tiles and passes from one end of the tile along the lowerchamber 58 to the opposite end with consequent evaporation of liquidfrom the wicking layer and cooling of the lower wall 50. On reaching theopposite end, the air flow is routed through apertures 19 into the upperchamber and flows towards outlet opening 21 along with air entering thatchamber through inlet opening 20 coupled with an upstream tile. The aircollected in the duct formed by the upper chambers 60 of each row oftiles is discharged at the downstream end of the duct to the return ductof an air conditioning system. The inlet opening 20 at the upstream endof the duct formed will be closed or absent from the corresponding tilewhile the outlet opening 21 at the opposite end of the duct will be openfor connection to an exhaust. Inlet 18 is not continuous across thewidth of ceiling tile 11 as this would disrupt the flow of liquid alongwick 5.

Tiles 11 can be placed directly onto T-bars as typically found incommercial buildings (see FIG. 5). In a modification, each tile unit ormodule 11 may be manufactured without the chamber 60; for instance, oncethe air has passed over the wicking layer 5 in each tile unit, it may bedischarged directly to atmosphere or to a common air return duct orducts or common plenum chamber separate from the tile units.

FIG. 4 illustrates one method of designing the feed and collectorassociated with the wicking layer in each tile unit. FIG. 4 is across-section perpendicular to direction of the flow of air. The liquidfeed is in the form of a supply wick 12 connected to a supply reservoir(not shown) so that supply wick 12 wets wicking layer 5 at a locationadjacent one edge thereof, supply wicks of adjacent ceiling tiles 11being connected in serial fashion so as to provide a continuous wickextending along a row of tiles and feeding the wicking layers 5associated with each of the tiles in the row. Connection of one feed orcollector wick to the next may be achieved for example simply byarranging for their ends to contact when the tiles are butted up to oneanother. The collector wick 13 is connected to a drainage container andserves to drain each of the wicking layers 5 of a row of tile units,such drainage being effected at a location adjacent the opposite edgesof the wicking layers to those edges connected to the supply wick 12.Supply wick 12 and collector wick 13 are separated from direct contactwith each other by separator 10 and are arranged to extend both upwardlyand in overlying relation with the bottom wall 50 so as to increase thecross-sectional area of the wicking material. The sections 12 a, 12 band 13 a, 13 b of the wicks 12 and 13 extending upwardly and inoverlying relation with the lower surface 3 are isolated from exposureto the exhaust air by intervening walls 70, 72. Walls 70 may becastellated at their lower edges or otherwise designed to permit contactbetween the wick 5 and wicks 12, 13 so as to maintain fluid flowcontinuity therebetween.

The embodiment of FIG. 5 is similar to that of FIG. 4 having a supplywick 17 and a collector wick 16 but in this case the wicks do not extendin overlying relation with the bottom wall 50. This embodimentillustrates how the tile units 11 may be mounted in a suspended falseceiling arrangement with each tile unit being supported around itsperimeter by T-bars 15 of the suspended ceiling system.

Preliminary calculations indicate the following. If the evaporation ratefrom wicking layer 5 is 0.01 g.s⁻¹.m⁻², corresponding to a thermal loadof approximately 25 W.m⁻², and the tiles 11 are 1 m long and 0.5 m wide,then the rate of evaporation from each tile 11 is 0.005 g.s⁻¹. If supplyreservoir 6 is located at ceiling level and collection container 7 islocated at floor level, the height from collection container 7 toreservoir 6 is approximately 2.5 m and the available forcing pressurefor the system is approximately 25 kPa. If we consider a strip ofceiling tiles 11 0.5 m wide with supply wick 17 and exhaust wick 16built into the sides of tiles 11 and of diameter 30 mm, the flow acrosstiles 11 will not be uniform but will be greatest through the tile 11nearest supply reservoir 6 and least at a distance more than halfwayalong the strip from supply reservoir 6. The actual distance of theminimum flow depends upon the ratio of the mass evaporated to the totalmass flow rate. If the mean flow through tiles 11 is twice the requiredflow for evaporation, thus limiting the concentration of any additivesto the water, the minimum flow rate is at approximately 0.67 of thelength of the strip from the supply end. If wick 5 is 1 mm thick and allwicks 5 have a permeability of 10⁻¹¹ m², which is typical for many clothfabrics, the forcing pressure of 25 kPa would ensure an adequate flow toall parts of a 5 m long strip of tiles 11. If tiles 11 were configuredwith supply wick 12 and collector wick 13 as in FIG. 4 and each had across-sectional area of 0.003 m², then-the strip of tiles 11 could be 10m long.

It will be understood that exhaust air 4 becomes more humid as it flowsfrom inlet 18 to outlet 19. Hence the heat transfer varies along tile 11and consequently the temperature of the ceiling varies along each tile.A more uniform ceiling temperature can be obtained by suitablydecreasing the height of the gap for exhaust air 4 as it travels alongthe tile from inlet 18 to outlet 19. Such an arrangement is implementedin the embodiment of FIG. 6 (which is a view corresponding to that ofFIG. 3) in that the cross-section of the lower chamber 58 reduces fromthe inlet end towards the outlet end, i.e. by inclining the intermediatewall 56 in the manner shown.

FIGS. 7A and 7B illustrate possible variations of the feeder/collectorarrangements for the wicking layer 5 in which the water feed andcollection is via a hollow pipe whereby the wicking layer 5 is wetteddirectly from the supply pipe rather than by capillary action through awick such as the wicks 12, 13 shown in FIG. 4 for example. In sucharrangements, it is important to ensure that the pipes are maintainedfilled with liquid so as to avoid air being drawn in and interruptingfluid flow.

In FIG. 7A, the feed/collector pipe 24 has a perforated wall and thewicking material 5 is wrapped in tubular fashion around the pipe so thatthe liquid supply passes through the perforations directly into thewicking material. The perforations are preferably provided at or in thelowermost regions of the wall of the pipe 24.

In FIG. 7B, the feed/collector pipe 25 comprises spaced apart first andsecond sections 25 a and 25 b with a spiral former 25 c bridging the twosections so that the wicking material can be wrapped in tubular fashionaround the assembly 25 a, 25 b, 25 c with the former 25 c supportingthat section of the wicking material spanning the sections 25 a, 25 b.In each case, an edge portion of the wicking layer 5 is wrapped aroundthe feed/collector pipe 24 or 25. Successive pipes 24, 25 associatedwith adjacent tile units may be coupled together via spigot and socketconnections which may automatically engage and seal together whenadjacent tiles are butted against one another. The wicking materialwrapped around the pipes may be arranged to overlap when the successivepipes are interengaged, to afford fluid flow continuity therebetween.

These pipe arrangements, as shown in FIGS. 7A and 7B, will not selfprime but can be filled simply by raising the water level in a reservoirat the time of commissioning the system. When the pipes are full ofwater, capillary forces in the wick will hold the water in placeprovided the distance from the bottom of the exhaust pipe to the highestpoint of the supply and exhaust pipes, is less than the height to whichthe wicks will raise water. A typical wicking height for cloth fabricsis 120 mm. Any ends of the wicks must be sealed onto the walls of thepipes to prevent air being drawn into the pipe between the wick and thesupporting structure. Calculation has shown that the main pressure dropin this system is across the wick, and 6 mm pipes in a 20 m strip oftiles would require a head of water of only 30 mm for a supply waterflow rate equal to twice the evaporation rate. This would allow thewater level in the supply reservoir to be 20 mm below the ceiling withthe end of the exhaust pipe approximately 60 mm below the uppermostpoint of the supply pipe, which is well within the wicking height oftypical cloth fabrics.

It will be understood that where tile modules or units are used, theymay be arranged in an array, e.g. a number of rows of tiles arrangedside-by-side with each row forming an air flow duct. Common inlet andoutlet headers may be associated with the array for routing air into andexhausting air from the ducts. Usually the air flow along one row oftile units will be separate from the air flow taking place in adjacentrows; however, we do not exclude the possibility of interconnectionsbetween the ducts associated with adjacent rows of tile units.

In a further modification of the invention, the units 11 may be ofelongated configuration in the direction of air flow, i.e. of strip-likeconfiguration. In this case, two or more strip units may beinterconnected in a serial fashion so as to extend across the space tobe cooled or a single such strip unit may span the space in onedirection (i.e. the direction of air flow through the units) and theremay be two or more such strip units located side-by-side so as to spanthe space in the direction perpendicular to the air flow direction. Whenthe units are in strip form, they may be manufactured in long lengthswith the wicking layer bonded to the bottom wall with liquid feed andcollector wick sections or pipes attached in situ, if desired togetherwith the upper chamber 60. This latter arrangement also applies to thecase where the units are in the form of tiles, i.e. individual tiles maybe provided with bonded wicking layers and/or in situ feed and collectorwick sections or pipes.

In the embodiment shown in FIG. 8, instead of one or more inlets 18being located at or adjacent one end of a tile unit, the tile unit mayhave inlets distributed at different points (extending through bothlower wall 50 and the wicking layer 5) to allow exhaust air 4 to passinto the unit at a range of locations between opposite ends of the unit.Likewise the intermediate wall 56 may, if desired, be provided withoutlets 19 distributed at various locations to provide an array of entrypoints from chamber 58 into chamber 60.

A numerical thermal model of the system has been developed and a smallexperimental model of the system has been built in the laboratory. Thenumerical model has been validated by comparing its results with thoseobtained from the laboratory experimental model. Simulations with thenumerical model have shown that the electric power consumption for airconditioning in large commercial buildings can be significantly reducedif the cooling system of the present invention is installed, primarilybecause the air flow rate in the system can be substantially reducedwith a corresponding reduction in power for pumping air through thecooling system and also reduction in compressor power.

Laboratory experiments with cotton wicks over a period of six monthshave shown that mould or fungal growth on the wick can be eliminatedwith saline solutions. Clearly, the proper use of appropriate fungicidescould also ensure that the system remains uncontaminated. If a salinesolution is used to prevent mould growth, it would also preventlegionella from contaminating the system because those bacteria requirenon-saline water to survive. Furthermore, since there is no sprayassociated with this system, there is no means for carrying legionellathrough the system. Mould growth would also be inhibited by the lack oflight within the enclosed tiles and an open cell foam insert could beused to prevent any light entering via the inlet or inlets.

Since the ceiling in this system is wet, it would serve to inhibit thespread of fire. If the water level in the supply reservoir wereincreased when fire was present in the building, then the ceiling wouldbe flooded and it could form an active part of the fire control systemof the building—viz. the fire detection system may be linked to thewater supply to the cooling system of the present invention so as toflood the normally wetted face of the cooling system in response todetection of a fire.

A 10% saline solution, which is similar to sea-water, has been used inthe laboratory to inhibit the growth of mould. Since the air leaving acooling ceiling system according to the present invention may be almostsaturated, the system can be used to provide fresh water from sea waterby desalination, for example in air-conditioned buildings. Sea watercould be delivered to an air-conditioned building and distributed to thecooled ceiling system, and the refrigeration plant of theair-conditioning system could be used to condense the water vapour fromthe nearly saturated return air and thereby generate fresh water,effectively as a by-product. Calculations indicate that if the thermalload dissipated through the ceiling system were 28 W/m² of floor area,then the system would produce approximately 1 liter of fresh water persquare meter of floor area for each 24 hour period of running.

In conventional air conditioning systems around 80% of the air isrecycled within the system, the remainder being vented to theatmosphere. The present invention facilitates use in the same manner,but is also able to use 100% fresh air, i.e. with no recycling. As theuse of recycled air has been linked with so called ‘sick buildingsyndrome’ the ability to use 100% fresh air may be advantageous, e.g.for air quality purposes.

In the embodiments described thus far, the cooling surface comprisespart of or forms a substantially uninterrupted wall structure (e.g.ceiling) bounding a space to be cooled. However, the bounding surfaceneed not be uninterrupted; it may be formed by a number of spacedsurfaces. Such spaced surfaces may collectively form a boundary of theenclosed space to be cooled. For example, they may form a false ceilingor overhead structure of slatted form. One embodiment which may be usedin such circumstances is illustrated in FIGS. 9 to 15 to which referenceis now made.

In this embodiment, a bank of spaced apart, generally parallelevaporating ducts 70 is mounted in overhead relation to the room orother space to be cooled, just below the roof 71. Each duct 70 comprisesan elongate member of generally U-shaped section comprising generallyvertically extending side walls 72 and a generally horizontal lower wall74. The open upper end of each member is closed by a liquid supplyarrangement 75 so that each duct 70 forms a channel for conducting airflow through the duct interior. At one end, each duct 70 is open so asto form an inlet for admission of air and at the opposite end it isconnected to a common plenum chamber 76 which may be mounted in thespace to be cooled or externally thereof The internal faces of the sideswalls 72 are provided with a layer 78 of wicking material such as acotton fabric so that a suitable liquid such as water can be wickedacross the internal surfaces thereby developing a layer of the liquid incontact with and wetting such surfaces. Although not shown in FIG. 11,the lower wall 74 may likewise be provided with a layer or otherstructure of wicking material on the inner surface 80 to allow a layerof the liquid to be developed across the lower wall 74 although asmentioned below, it is not essential to do this. The wicking material 78and on surface 80 will usually extend over substantially the fall lengthof each duct 70.

Liquid is supplied to the wicking structures 78 and on surface 80 (ifpresent) by the arrangement 75 which in this case comprises a deliverytube 82 of wicking material over which a cover 84 is provided to preventevaporation of liquid into the surroundings. The wicking tube 82 extendsover substantially the entire length of the associated duct 70 so thatthere is a supply of liquid to the top edges of the wicking layers 78along substantially the entire length of the duct. The tube 82 at oneend dips into a liquid reservoir 86 and the arrangement is such that thehighest open point on the liquid delivery tube 82 should not exceed thewicking height of the wick (typically about 150–200 mm).

Once the wicking tube 82 and the wicking structures 78 and on surface 80have been primed with liquid, it will be seen that the walls 72 and 74can be maintained continuously wetted while preventing dripping if theliquid level in the reservoir 86 is appropriately positioned, viz. belowthe lower edges of the vertically arranged wicking layers 78. There maybe one reservoir 86 associated with each delivery tube 82 or a number ofwicking tubes 82 may be serviced by a single reservoir 86, e.g. all ofthe wicking tubes 82 may be supplied by a single common reservoir 86.

In operation, air from the space to be cooled flows through ducts 70from the inlet ends 77 thereof to the plenum chamber 76 from where itmay be exhausted. The air flow is created by developing a pressuredifferential between the space to be cooled and the interiors of theducts 70. This can be effected for example by means of a fan (not shown)connected to the plenum chamber 76 and arranged to suck air from thespace to be cooled into the ducts, or it may be created by developing apositive pressure, which need only be relatively small, within the spaceto be cooled so that the resulting pressure differential is effective toinduce the desired air flow. Air flow through the ducts 70 results inevaporation of liquid from the wicking structures 78 and on surface 80thereby cooling at least the sides walls 72 and also the bottom wall 74(if surface 80 is provided with wicking structure). These walls in turnserve to cool air circulating, e.g. vertically downwards (or upwards),past their external surfaces with consequent cooling of the space inwhich the cooling system is installed. The external air flow may be aforced flow, e.g. created by a blower or blowers, or it may be theresult of natural circulation of the air.

The ducts may be fabricated from suitable plastics material or frommetal. Where the lower wall 74 has a relatively small width comparedwith the height of the walls 72, the wicking layer or structureassociated with wall 74 may be omitted without significantly affectingcooling power, even more so if the ducts 70 are fabricated from materialhaving good thermal conductivity such as a suitable metal. Typicaldimensions for the ducts 70 are:

Side walls 72—50 mm up to 200 mm, e.g. 100 mm

Bottom wall 74—6 to 24 mm, e.g. 12 mm

-   -   Pitch between adjacent ducts (centre line to centre line)—15 to        35 mm, e.g. 25 mm

In FIG. 9, a single bank or array of ducts is illustrated; however, itwill be appreciated that there may be more than one array of ductshaving the same function disposed one above the other to give anincreased thermal performance and/or to produce a desired visual effect.The arrangement may be such that the ducts in one array aresubstantially vertically aligned with those in the adjacent array(s) orthe ducts in adjacent arrays may be staggered, for example so that theducts in one array overlie the spaces in the adjacent array. In such anarrangement, each array may have to be provided with its own supplyreservoir because of wicking height considerations.

The arrangement shown in FIG. 11 is suitable for situations where thereis no risk of material precipitating from the liquid, e.g. water orwater containing a liquid biocide. However, if there is a risk of suchprecipitation, as would be the case where the liquid incorporates asolid, soluble biocide (such as NaCl) or other additive dissolvedtherein, it may be desirable to ensure that crystallisation of thesolute is prevented at the extremities of the wicking material, e.g. thelower edges of the layers 72. This may be achieved by providing a liquidcollector at the bottom of each duct 70 which, as illustrated in FIG.11A may be in the form of a wicking tube 90 arranged to collect and feedthe liquid to a collection vessel 92 suitably arranged with its liquidlevel below the supply reservoir 86 (see FIG. 12). Liquid collected inthe collection vessel 92 may be recycled to the supply reservoir 86. Asingle collection vessel 92 may service all of the collecting tubes 90or more than one collection vessel 92 may be provided with each vesselservicing two or more collecting tubes 90. Although not illustrated inFIG. 11, there may also be a layer of wicking material on the internalsurface of the wall 74.

A liquid delivery tube 82 may be arranged to feed the liquid to morethan one duct 70. One such arrangement is illustrated in FIG. 13 inwhich pairs of ducts 70 are fed by a single U-shaped delivery tube 82which has one leg 94 overlying and sealing the upper open end of oneduct 70 and a parallel leg 96 overlying an adjacent duct 70, the legs 94and 96 being interconnected by bight portions 98 and having their freeends dipping into the supply reservoir 86. The collector tubes 90 may besimilarly configured so as to extend over more than one duct 70, e.g. apair of adjacent ducts, and thereby collect liquid to the collectorvessel 92. The bight portion 98 of the delivery or collector tube mayprovide continuity of wicking feed between the legs 94 and 96.

The delivery tubes and/or the collection tubes 90 may advantageously befabricated in the manner illustrated in FIGS. 14 and 15 in which a layerof wicking material 100, e.g. cotton fabric, is wrapped around asupporting tube 102 e.g. of a plastics material which is produced with alongitudinal slit 104 through which the wicking material can beinserted. The plastics material may be of a resilient nature such thatthe slit tends to be closed when the tube is unstressed but can beforced open for the purpose of inserting the wicking material. Insertingthe wick into the split 104 maintains the gap when the wick is wrappedaround the pipe and overlapping the wick at the gap ensures that thepipe is sealed from air when the wick is wet. The gap would for examplebe 0.1 mm if the wick were 0.1 mm thick and if the tube 102 were 12 mmin diameter, typically a suction of 1500 Pa could be supplied at one endof a 4 m long, dry pipe to draw water from a reservoir 150 mm below thepipe. The leakage of air into the tube through the dry wick would beinsufficient to prevent the water from being drawn along the wholelength of the wick. The tube 102 can then be filled with water and thewick wetted to feed the evaporating ducts 70. Since the arrangement maybe such that the tube 102 is always below atmospheric pressure, thisallows the whole system to be charged with water with no possibility ofany drips forming. This is very important if the system is installed insituations where no interruption in the use of a room can be tolerated,such as a telephone exchange. One end of the tube 102 is dipped into theliquid supply reservoir while the opposite end may either be sealed(after filling) or dip into a pool of liquid which may be the supplyreservoir 86 or another liquid reservoir which could be at a slightlylower level so as to induce flow through the tube 102 from the higherreservoir to the lower reservoir. Such an induced flow is not essentialbut may aid in checking that liquid flow is taking place (as observedvia a transparent section of tubing) and it may serve to sweep away anygas bubbles that may arise from desorption from the liquid.

Air ingress into the delivery and/or collection tubes 82, 90 should beavoided for efficient operation. To provide wick sealing at the ends ofthe tubes 82, 90, heat shrink tubing 110 may be used as illustrated inFIG. 14 at those ends where the wicking tubes dip into the reservoirs86, 92. Where the tubes 82, 90 are U-shaped as in the embodiment of FIG.13, the bight portions 98 may be formed by tubing 110 linking the twolegs 94, 96 of a wicking tube together.

The cooling system described herein is not limited in its use merely tobuildings, but could also be used in vehicles such as cars, coaches,refrigerated lorries, ships, trains and aeroplanes and other enclosureswhere cooling may be required.

Whilst endeavouring in the foregoing specification to draw attention tothose features of the invention believed to be of particular importance,it should be understood that the Applicant claims protection in respectof any patentable feature or combination of features disclosed hereinand/or shown in the drawings whether or not particular emphasis has beenplaced on such feature or features. Moreover, it will be appreciatedthat certain features of the invention which are, for clarity, describedin the context of separate embodiments, may also be provided incombination in a single embodiment. Conversely, various features of theinvention which are, for brevity, described in the context of a singleembodiment may also be provided separately or in any suitablesub-combination. For instance, while the feature of FIG. 6(cross-sectional change) is not illustrated for the embodiment of FIG.11 and variations thereof, it will be appreciated that this, and otherfeatures disclosed herein, are applicable to the embodiment of FIG. 11and variations thereof

1. A cooling unit forming an air flow channel for cooling an enclosedspace, said cooling unit comprising a wall having internal and externalfaces, said external face at least partially defining said enclosedspace to be cooled, with at least one opening for air to communicatebetween the internal face and the external face, a layer of wickingmaterial for developing a layer of liquid on the internal face forexposure of the layer of liquid to and evaporation into air-flow fromthe external face into exhaust air coming from the enclosed spacethrough the at least one opening to cause cooling of the external faceof the wall, and a liquid supply reservoir arranged so that a liquidlevel is below the layer of wicking material, supply of liquid to thewicking material from the liquid supply reservoir being maintained bywicking action, the wicking material comprising a number of discretesections.
 2. The unit as claimed in claim 1, wherein at least some ofthe discrete sections share at least one of a common liquid feed and acollector.
 3. A cooling unit comprising a duct forming an air-flowpassageway having an internal surface and an external surface thereofwith at least one opening for air to communicate between the internalsurface and the external surface and provided with a layer of wickingmaterial by which a layer of liquid in contact with said internalsurface is developed and from which evaporation is induced by air flowthrough the duct from the external surface, and a liquid supplyreservoir arranged so that the liquid level is below the layer ofwicking material, supply of liquid to the wicking material from theliquid supply reservoir being maintained by wicking action, the ductincluding a liquid delivery wicking element for supply of liquid to oneedge of the layer of wicking material, the duct including a member ofU-section, an open side of which being closed by the liquid deliverywicking element.
 4. The unit as claimed in claim 3, wherein said elementcomprises a tube of wicking material.
 5. The unit as claimed in claim 4,wherein the tube of wicking material is provided on a supporting tube.6. The unit as claimed in claim 5, wherein the wicking material iswrapped around the supporting tube and inserted through a slit in thesupporting tube.
 7. The unit as claimed in claim 6, wherein thesupporting tube is at least partially filled with liquid for supply tothe wicking material.
 8. A cooling unit comprising a duct forming anair-flow passageway having an internal surface and an external surfacethereof with at least one opening for air to communicate between theinternal surface and the external surface and provided with a layer ofwicking material by which a layer of liquid in contact with saidinternal surface is developed and from which evaporation is induced byair flow through the duct from the external surface, and a liquid supplyreservoir arranged so that the liquid level is below the layer ofwicking material, supply of liquid to the wicking material from theliquid supply reservoir being maintained by wicking action, the ductbeing provided with a liquid collecting wicking element for conductingliquid from the wicking material on said internal surface to a liquidcollection point.
 9. A cooling unit comprising a duct forming anair-flow passageway having an internal surface and an external surfacethereof with at least one opening for air to communicate between theinternal surface and the external surface and provided with a layer ofwicking material by which a layer of liquid in contact with saidinternal surface is developed and from which evaporation is induced byair flow through the duct from the external surface, a liquid supplyreservoir arranged so that the liquid level is below the layer ofwicking material, supply of liquid to the wicking material from theliquid supply reservoir being maintained by wicking action, and across-sectional area of a path of the air flow varying in a direction ofair flow.
 10. The unit as claimed in claim 9, wherein thecross-sectional area of the air flow path is progressively reduced inthe downstream direction of air flow.
 11. A system for use in cooling anenclosed space, said system comprising a plurality of units each havinga duct forming an air flow passageway having an internal surface and anexternal surface thereof with at least one opening for air tocommunicate between the internal surface and the external surface andprovided with a layer of wicking material by which a layer of liquid incontact with said internal surface is developed and from whichevaporation is induced by air flow through the duct from the externalsurface, the units being arranged to conduct air flow in at least one ofserial and parallel fashion, a liquid supply reservoir arranged so thatthe liquid level is below the layer of wicking material, supply ofliquid to the wicking material from the supply reservoir beingmaintained by wicking action, and a chamber for producing a flow of airthrough the duct, the chamber for producing the air flow being a plenumchamber or chambers into which air removed from the enclosed space ispassed for discharge externally of the enclosed space.
 12. A coolingsystem for an enclosed space, said cooling system comprising: a surfacestructure exposed to air within the enclosed space, a layer of wickingmaterial developing a layer of liquid on a remote face of the surfacestructure remote from the space, a device exhausting air from thesurface structure exposed to air within the enclosed space and passingthe exhausted air over said remote face remote from the space so that,in use, the exhaust air effects evaporation of liquid from said layerthrough the surface structure into the air flow, and a liquid supplyreservoir arranged so that a liquid level is below the layer of wickingmaterial, supply of liquid to the wicking material from the liquidsupply reservoir being maintained by wicking action.
 13. The system asclaimed in claim 12, wherein the surface structure comprises a pluralityof units having a duct forming an air-flow passageway having an internalsurface or surfaces thereof provided with the layer of wicking materialby which a layer of liquid in contact with said internal surface isdeveloped and from which evaporation is induced by air flow through theduct and the plurality of units are arranged in at least one of serialfashion and parallel side by side fashion.
 14. The system as claimed inclaim 13, wherein the units are of elongated configuration.
 15. Thesystem as claimed in claim 13, wherein each unit includes a furthersurface in spaced, opposed relation to said remote face to form an airflow path across said remote face.
 16. The system as claimed in claim13, wherein the internal face of each cooling unit is provided with thelayer of wicking material and at least some of the cooling units areinterconnected so that liquid flow is conducted from the layer ofwicking material of one unit to the layer of wicking material of thenext unit.
 17. The system as claimed in claim 13, further comprising achamber for discharge of air after passage over the liquid layer and thechambers of at least some of the units are interconnected to form an airdischarge duct.
 18. A method of cooling an enclosed space by contactingair with said space with at least one surface structure, said methodcomprising the steps of: feeding liquid to a layer of wicking materialso as to develop a layer of liquid on a surface of said structure whichis remote from said space; and removing air from the space andcontacting the air removed from the space with the liquid layer remotefrom the space so that evaporation of liquid from the liquid layer intothe air flow is secured thereby cooling said structure and hence thespace bounded thereby, the liquid being fed to the layer of wickingmaterial from a liquid supply reservoir arranged so that the liquidlevel is below the layer of wicking material, supply of liquid to thewicking layer from the supply reservoir being maintained by wickingaction.
 19. The method of claim 18, wherein the liquid includes anadditive to inhibit microbial growth.
 20. The method of claim 18,wherein sea water is used as the liquid and vapor entrained in the airflow is collected and condensed for use as fresh water.